"Although there doesn't appear to be any one mission that justifies the X-37B program, the ability to flight-test new sensors and hardware before they go into full development, combined with a more timely, flexible way to conduct surveillance, is why I think this program is going forward," says former Air Force Space and Missile officer Brian Weeden, the report's primary author.

The Pentagon used to turn to the Space Shuttle from time to time to deliver spy satellites into orbit. But the Shuttle is about to be retired. Enter the X-37B – an unmanned, smaller-scale version of the reusable spacecraft. Not only can it carry signals and intelligence sensors in its payload bay. But because it can stay in space for weeks or months at a time, the X-37B can give those new sensors time to be put into action.

The "ability to re-configure the payload bay contents for various sensor packages would make it much more flexible than having to procure multiple satellites," the report notes. And "once in orbit," the X-37B could be much more maneuverable than current or planed satellites, "allowing for more flexible ground coverage."

"Imagine there's a flareup in one particular corner of the world," Weeden adds. "The battlefield commander there needs a certain space ISR [intelligence surveillance reconnaissance] capability. You can slap those sensors from a rack into the X-37B and fire away."

Other missions are far less likely, Weeden believes. Repairing (or screwing with) satellites in orbit would be tough – "not many existing operational military satellite components will fit in the X-37B cargo bay," the report notes.

Dropping bombs from the X-37B seems even more far-fetched. "Weapons dropped from [its] bay would need to be equipped with thrusters capable of performing a huge deorbit burn, [which would be] very difficult given [the space plane's] small bay size," according to the report. What's more, "X-37B after re-entry would be a slow moving, not-very-maneuverable glide bomb, easy prey for any air defense system along its path to the target.... [and] having only few X-37Bs would not provide very timely coverage of potential ground targets."

Not that the United States has ruled out space weapons entirely. "My sense is there is not going to be a great tolerance for a significant offensive capability in space," General James Cartwright told a Washington symposium yesterday. "The question is, what’s the right balance between defense and offense in space?"

The X-37B will almost certainly play a role in that debate – just not as a bomb-dropper.